Preparation and structural characterization of a platinum catecholate complex containing two 3-ethynylthiophene groups

Article abstract of DOI:10.1021/om950155t

The reaction of 1,2-bis(tert-butyldimethylsiloxy)-3,4-bis(3-ethynylthiophene-yl)benzene (4) with Pt-(P(Ph)₃)₂Cl₂ and tetrabutylammonium fluoride produces a novel platinum catecholate complex.

Full text of DOI:10.1021/om950155t

460
Organometallics 1996, 15, 460-463
P r ep a r a tion a n d Str u ctu r a l Ch a r a cter iza tion of a
P la tin u m Ca tech ola te Com p lex Con ta in in g Tw o
3-Eth yn ylth iop h en e Gr ou p s
J ames D. Kinder*
NASA Lewis Research Center, Cleveland, Ohio 44135
Wiley J . Youngs
Department of Chemistry, The University of Akron, Akron, Ohio 44325
Received February 27, 1995X
Sch em e 1
Summary: The reaction of 1,2-bis(tert-butyldimethylsi-
loxy)-3,4-bis(3-ethynylthiophene-yl)benzene (4) with Pt-
(P(Ph)3)2Cl2 and tetrabutylammonium fluoride produces
a novel platinum catecholate complex.
The catechol group can coordinate to a variety of
transition and main group metals in a wide range of
oxidation states.1 Catechols and metal catecholates
have been intensively studied for their unique struc-
tural,2 electronic,3 magnetic,4 and catalytic activity.5 The
incorporation of metal catecholates into a conducting
polymer matrix provides the opportunity for the con-
struction of modified electrodes that may have interest-
ing electrocatalytic behavior. In this paper, the syn-
thesis, characterization, and electrochemical properties
of a platinum catecholate complex containing two
3-ethynylthiophene groups are described.
The synthesis of the platinum catecholate complex 5
is illustrated in Scheme 1. The synthesis of 1 was
accomplished by the procedure developed by Kajigaeshi
and co-workers.6 Treatment of 1 with BBr3 in acetic
acid produced the diiodocatechol 2 (94% yield). To
prevent the catechol group from complexing the pal-
ladium catalyst used in the alkyne coupling reaction,
the catechol was protected by reacting 2 with tert-
butyldimethylsilyl chloride to form 3 (69% yield). The
tert-butyldimethylsilyl group was chosen due to its
reported stability to a variety of reaction conditions and
its facile removal by fluoride ion.7 Reaction of 3 with 2
equiv of 3-ethynylthiophene8 in the presence of a pal-
ladium catalyst produced the disubstituted product 4
(62% yield).
X Abstract published in Advance ACS Abstracts, October 15, 1995.
(1) (a) Pierpont, C. G.; Buchanan, R. M. Coord. Chem. Rev. 1981,
38, 45. (b) Blatchford, T. P.; Chisholm, M. H.; Huffman, J . C. Inorg.
Chem. 1988, 27, 2059. (c) Kaim, W. Coord. Chem. Rev. 1987, 76, 187.
(2) (a) Churchill, M. R.; Lake, C. H.; Paw, W.; Keister, J . B.
Organometallics 1994, 13, 8. (b) Zirong, D.; Bhattacharya, S.; Mc-
Cusker, J . K.; Hagen, P. M.; Hendrickson, D. N.; Pierpont, C. G. Inorg.
Chem. 1992, 31, 870. (c) Karpishin, T. B.; Stack, T. D. P.; Raymond,
K. N. J . Am. Chem. Soc. 1993, 115, 182.
(3) (a) Bhattacharya, S.; Pierpont, C. Inorg. Chem. 1992, 31, 35. (b)
Dilworth, J . R.; Ibrahim, S. K.; Khan, S. R.; Hursthouse, M. B.;
Karaulov, A. Polyhedron 1990, 9, 1323. (c) Lever, A. B. P.; Auburn,
P. R.; Dodsworth, E. S.; Haga, M.; Liu, W.; Melnik, M.; Nevin, W. A.
J . Am. Chem. Soc. 1988, 110, 8076. (d) Bhattacharya, S.; Boone, S.
R.; Fox, G. A.; Pierpont, C. J . Am. Chem. Soc. 1990, 112, 1088.
(4) (a) Coucouvanis, D.; J onasdottir, S. G.; Christodoulou, D.; Kim,
C. G.; Kampf, J . W. Inorg. Chem. 1993, 32, 2987. (b) Gojon, E.; Latour,
J .; Greaves, S. J .; Povey, D. C.; Ramdas, V.; Smith, G. W. J . Chem.
Soc., Dalton Trans. 1990, 2043.
(5) (a) Haga, M. Inorg. Chem. 1986, 25, 447. (b) Persson, C.;
Andersson, C. Polyhedron 1993, 12, 2569. (c) Takacs, J .; Kiprof, P.;
Riede, J .; Herrmann, W. Organometallics 1990, 9, 782. (d) Ueda, C.;
Tse, D. C.; Kuwana, T. Anal. Chem. 1982, 54, 850. (e) J aegfeldt, H.;
Torstensson, A. B. C.; Gorton, L. G. O.; J ohansson, G. Anal. Chem.
1981, 53, 1979. (f) Barbaro, P.; Bianchini, C.; Linn, K.; Mealli, C.;
Meli, A.; Vizza, F.; Laschi, F.; Zanello, P. Inorg. Chim. Acta 1992, 198-
200, 31.
The formation of metal catecholates normally pro-
ceeds by treating a catechol with strong base (e.g., KOH)
in the presence of a metal dichloride. However, the
platinum catecholate complex 5 formed in high yield
(94%) by combining 4 with a THF solution of tetra-n-
butylammonium fluoride and Pt(PPh3)2Cl2. Thus, it
was unnecessary to deprotect 4 to form the catechol
before reaction with the metal dichloride. The infrared
spectrum of 5 showed an intense absorption at 1284
cm-1, indicating a C-O stretching vibration, which is
indicative of a metal catecholate structure. The thermal
stability of 5 was examined with thermal gravimetric
analysis (TGA). A 5% weight loss was observed for 5
at 307 °C in N2.
(7) (a) Corey, E. J .; Venkateswarlu, A. J . Am. Chem. Soc. 1972, 94,
6190. (b) Core, E. J .; J ones, G. B. J . Org. Chem. 1992, 57, 1028. (c)
Corey, E. J .; Yi, K. Y. Tetrahedron Lett. 1992, 33, 2289.
(6) Kajigaeshi, S.; Kakinami, T.; Moriwaki, M.; Watanabe, M.;
Fujisaki, S.; Okamoto, T. Chem. Lett. 1988, 795.
(8) Youngs, W. J .; Solooki, D.; Tessier, C. A. Synlett 1990, 427.
0276-7333/96/2315-0460$12.00/0 © 1996 American Chemical Society

Notes
Organometallics, Vol. 15, No. 1, 1996 461
F igu r e 2. Cyclic voltammogram of 5 (1 mM) in 0.1 M
TBAP-CH2Cl2. Scan rate was 100 mV s-1
.
Exp er im en ta l Section
Ma ter ia ls. All manipulations were performed using stan-
dard inert atmosphere techniques10 unless otherwise specified.
Literature procedures were used to prepare 4,5-diiodovera-
trole,6 3-ethynylthiophene,8 and dichlorobis(benzonitrile)pal-
ladium(II).11 Diisopropylamine was distilled from BaO, CH2Cl2
from CaH2, and tetrahydrofuran (THF) from sodium-ben-
zophenone ketyl. Tetrabutylammonium perchlorate (TBAP,
Kodak) was recrystallized twice from ethyl acetate-pentane
and dried for 48 h at 100 °C (10-3 Torr) before use.
F igu r e 1. Thermal ellipsoid of 5 drawn at 50% probability.
Selected bond distances (Å) and angles (deg): Pt-O(1),
2.028 (8); Pt-O(2), 2.052(9); C(6c)-O(2), 1.333(16); C(1c)-
O(1), 1.348(15); P(1)-Pt-O(2), 87.9(3); P(2)-Pt-O(1), 90.5-
(3); P(2)-Pt-P(1), 98.6(1).
Crystals of 5 were grown by slow concentration of 5
in methylene chloride. The crystal structure of 5,
showing the thermal ellipsoids, is shown in Figure 1. A
molecule of methylene chloride is also present in the
asymmetric unit. Crystals of 5 were air stable. How-
ever, the crystals slowly lost solvent over time, which
degraded the quality of the crystals. The geometry of
the ligands around the platinum atom is square planar.
The thiophene ring containing sulfur atom S1 is twisted
(57.7°), and the thiophene ring containing sulfur atom
S2 is twisted (29.6°) out of the plane defined by the
platinum catecholate structure. The Pt-O bond dis-
tances of 2.028(8) and 2.052(9) Å and the C-O bond
distances of 1.348(15) and 1.333(16) Å are typical for
metal catecholate complexes.
Many thiophene systems can be anodically electropo-
lymerized to form electrically conducting polymers with
conductivities as high as 102 (Ω‚cm)-1. Substituents in
the â position on the thiophene ring have a strong
influence on both the conductivity and the extent of
polymerization of the thiophene monomers. Roncali and
co-workers found that when a bulky substituent such
as an isopropyl group is attached to the â position on
the thiophene ring polymerization can be prevented. By
adding two (CH2) units as spacers between the thiophene
and isopropyl groups, polymerization occurred.9
The cyclic voltammetry of 5 in 0.1 M TBAP-CH2Cl2
is shown in Figure 2. Two one-electron reversible (∆E
) 82 mV, ia/ic ) 1) oxidation waves at 0.266 and 0.870
V [vs Ag/Ag+ (CH3CN)] were observed. Attempts at
electropolymerization of 5 failed in CH2Cl2 and in a
mixture of 1:1 CH2Cl2-nitrobenzene. This may be due
to steric effects around the thiophene rings. Future
work will concentrate on synthesizing new metal cat-
echolate complexes analogous to 5 and examining the
electrochemical and optical properties of these new
systems.
Ap p a r a tu s. NMR spectra were recorded on either a Bruker
AC200 or AM300 spectrometer. X-ray diffraction data were
collected on a Syntex P21 single-crystal diffractometer. IR data
were collected on a Nicolet 510P FT-IR spectrometer. An
EG&G Princeton Applied Research Model 273A potentiostat/
galvanostat controlled by the EG&G Princeton Applied Re-
search Model 270 software package was used to monitor the
electrochemical measurements. Mass spectra were recorded
on a Kratos MS25RFA mass spectrometer. Thermogravimet-
ric analysis was collected on a Perkin-Elmer TGS2-II thermal
gravimetric analyzer.
Syn th esis of 4,5-Diiod oca tech ol (2). 4,5-Diiodoveratrole
(10.074 g, 26 mmol) was dissolved in CHCl3 and cooled to -60
°C. BBr3 (9.72 mL, 103 mmol) was slowly added via syringe.
After warming to room temperature the mixture was allowed
to stir for 6 h and was then poured into ice water. The product
was extracted with ether and dried with MgSO4. Evaporation
of the solvent produced 8.75 g (94% yield) of 2 as a white
powder. 1H NMR (acetone-d6, 200 MHz): δ 8.41, 7.35. 13C
NMR (acetone-d6, 300 MHz): δ 147.47, 126.50, 94.50. FT-IR
(KBr): 3245(s), 3048(m), 1595(m), 1477(s), 1408(s), 1307(m),
1224(s), 870(s), 701(s) cm-1
361.8294.
. HRMS calcd 361.8300, obsd
Syn th esis of 1,2-Bis(ter t-bu tyld im eth ylsilyloxy)-4,5-
d iiod oben zen e (3). A solution of imidazole (8.411 g, 124
mmol) and tert-butyldimethylsilyl chloride (9.32 g, 62 mmol)
dissolved in 50 mL of DMF was added via cannula to 11.193
g (31 mmol) of 4,5-diidocatechol dissolved in 100 mL of DMF.
After stirring for 48 h the mixture was poured into water,
extracted with ether, and dried with MgSO4. Evaporation of
the solvent followed by column chromatography on silica gel
eluting with hexane produced 12.54 g (69% yield) of 3 as a
white powder. 1H NMR (acetone-d6, 200 MHz): δ 7.38, 0.99,
0.23. 13C NMR (acetone-d6, 300 MHz): δ 148.86, 132.15, 97.14,
26.29, 19.12, -3.94. FT-IR (neat): 2955(s), 2930(s), 2858(s),
1564(w), 1542(m), 1472(s), 1390(m), 1338(s), 1292(s), 1255(s),
1005(w), 932(s) cm-1. HRMS calcd 590.0030, obsd 590.0027.
(9) (a) Roncali, J .; Garreau, R.; Yassar, A.; Marque, P.; Garnier, F.;
Lemaire, M. J . Phys. Chem. 1987, 91, 6706. (b) Roncali, J .; Garreau,
R.; Delabouglise, D.; Garnier, F.; Lemaire, M. Synth. Mett. 1989, 28,
C341.
(10) Shriver, D. F. The Manipulation of Air Sensitive Compounds;
R. E. Krieger Publishing Co.: Malabar, FL, 1982.
(11) Hartly, F. R. Organomet. Chem. Rev. A 1970, 6, 119.

462 Organometallics, Vol. 15, No. 1, 1996
Notes
Ta ble 1. Cr ysta llogr a p h ic Da ta for 5
Ta ble 2. Atom ic Coor d in a tes (×105) a n d
Equ iva len t Isotr op ic Disp la cem en t Coefficien ts
formula
C55H40Cl2O2P2PtS2
1124.9
P21/c
(Å2 × 104)
formula wt
space group
crystal system
cell constants
a (Å)
x
y
z
U(eq)a
630(3)
monoclinic
Pt(1)
P(2)
P(1)
O(2)
C(5B)
O(1)
C(1D)
C(2I)
C(3)
20807(3)
18558(20)
18123(21)
23500(50)
9618(4)
6912(27)
25779(26)
10499(61)
7994(3)
-3323(18)
7434(17)
18575(45)
-4173(72)
10237(44)
-9074(65)
52647(74)
45314(101)
666(15)
665(14)
686(38)
803(69)
681(38)
583(55)
703(66)
807(81)
741(68)
742(65)
785(69)
731(69)
586(57)
711(64)
659(58)
736(68)
976(78)
776(68)
709(65)
812(66)
752(67)
678(65)
775(62)
728(70)
761(66)
798(67)
1020(81)
736(67)
703(65)
668(56)
609(60)
791(70)
783(66)
665(65)
800(70)
626(54)
699(63)
658(60)
850(72)
688(62)
723(61)
660(57)
745(66)
654(60)
831(70)
801(70)
777(68)
824(72)
627(61)
740(63)
789(66)
940(82)
757(74)
1001(88)
18.556(4)
b (Å)
13.562(3)
c (Å)
20.524(4)
18993(83) -22866(116)
â (deg)
110.69(3)
4832(2)
24250(48)
8411(70)
-4567(63)
6961(87)
V (Å3)
Z
4
42223(73) -10296(107)
D (calcd) (g cm-3
)
1.546
3.221
2240.00
39736(85)
6547(85)
-9300(100)
absorp coeff (mm-1
F(000)
)
C(2D)
C(2H)
C(5A)
C(5D)
C(1A)
C(6B)
C(2A)
C(2)
C(1I)
C(6A)
C(3C)
C(6E)
C(3A)
C(4C)
C(1H)
C(4)
4222(95) -15897(72)
47971(82) -39381(102)
35427(71)
-6851(74)
temp (K)
133
22215(85)
-5006(84)
16986(70)
43799(109)
7916(98) -10702(79)
32929(85)
2θ range (deg)
scan type
3.5-45.0
ω
-394(67)
-2932(66)
-6114(68)
30134(75)
56104(82)
-740(80)
27267(73)
13561(75)
scan speed (deg/min in ω)
scan range (ω) (deg)
no. of reflns collcd
no. of indep reflns
refinement method
no. of obsd reflns
no. of params refined
R(F) (%)
8.72
1.80
4976
1771(79) -13208(113)
10315(73) 32213(96)
39458(89) -23829(125)
42642(88) -18993(130)
38662(103)
35046(74) -15415(107)
3984 (Rint ) 2.74%)
full-matrix least-squares
3362 (F > 4.0σ(F))
578
5.86
7.33
1.14
22941(88)
7302(80)
9512(86)
34203(73)
22282(115)
37239(105) -12243(77)
-7900(103)
Rw(F) (%)
31521(74)
40175(72)
39107(89)
7619(75)
-7379(75)
57513(82)
-7942(74)
-6264(72)
9520(64)
GOF
46397(75) -45476(108)
37378(78)
5670(85)
-8521(98)
37679(104)
C(2E)
C(4B)
C(3I)
C(2B)
C(6D)
C(1E)
C(1C)
C(4D)
C(3D)
C(6C)
C(1)
Syn th esis of 1,2-Bis(ter t-bu tyld im eth ylsilyloxy)-4,5-
bis(3-eth yn ylth iop h en e-yl)ben zen e (4). Diisopropylamine
(150 mL) was added to 0.4547 g (1.2 mmol) of Pd(Cl)2(PhCN)2,
0.6224 g (2.4 mmol) of PPh3, 0.1142 g (0.6 mmol) of CuI, and
7.0 g (12 mmol) of 3. To this solution was added 2.8 g (26
mmol) of 3-ethynylthiophene slowly via syringe. The mixture
was heated to 60 °C for 1 h and then cooled to room
temperature and stirred for 11 h. The mixture was filtered
and the solvent was evaporated. Chromatography on silica
gel eluting with a 1:9 CH2Cl2-hexane mixture produced 4.0465
g (62% yield) of 4 as a yellow powder. 1H NMR (acetone-d6,
300 MHz): δ 7.70 (dd, 1 H), 7.53 (dd, 1 H), 7.21 (dd, 1 H), 7.05
(s, 1 H), 1.02 (s, 9 H), 0.28 (s, 3 H). 13C NMR (acetone-d6, 300
MHz): 148.42, 130.57, 129.63, 127.00, 123.29, 120.40, 88.22,
26.22, 26.37, 19.15, -3.74. FT-IR (KBr): 3106(w), 2954(s),
2930(s), 2858(s), 1594(w), 1529(s), 1494(s), 1492(s), 1362(w),
24268(83) -24697(109)
44660(97)
26387(81)
2758(86)
-2630(124)
-7682(107)
8665(86)
28727(112)
-5696(98)
9523(69)
27508(67)
-6863(82)
-1222(82)
26941(70)
17191(69)
5477(110) -17469(82)
3414(106) -20059(71)
2131(111)
21446(71)
32372(75)
-4905(62)
28542(73)
19962(71)
-9207(78)
43548(94) -30578(121)
C(1B)
C(5C)
C(2C)
C(3B)
C(4A)
C(3H)
C(2F)
C(1G)
C(6F)
C(3F)
C(2G)
C(5F)
C(5E)
C(1F)
C(6G)
C(5G)
21253(76)
30215(70)
31401(72)
-5629(97)
963(104)
-14224(97)
28080(80) -17232(123)
42824(100) -12644(67)
54595(76) -42910(105)
15428(84)
34116(67)
-2541(66)
14101(67)
32002(74)
26041(82)
21702(78)
36895(84)
24963(91)
26944(90)
1125(85)
24317(75)
33495(83)
39689(82)
15851(97)
31903(105)
18666(88) -13370(72)
21037(117)
39716(107)
23582(102) -15782(78)
24549(1109)
14644(91)
28844(102)
32987(107)
40770(134)
1331(s), 1255(s), 932(s), 838(s), 781(s) cm-1
550.1852, obsd 550.1840.
. HRMS calcd
-5024(83)
18209(82)
Syn th esis of [4,5-Bis(3-eth yn ylth iop h en e-yl)-1,2-ben -
zen ed iola to(2-)-O,O′]bis(tr ip h en ylp h osp h in e)p la tin u m -
(II) (5). THF (20 mL) was added to a flask containing 1.001
g (1.8 mmol) of 4 and 1.437 g (1.8 mmol) of Pt(P(Ph)3)2Cl2. A
sample of 7.2 mL of a 1 M tetrabutylammonium fluoride-THF
solution was added via syringe. The mixture was allowed to
stir for 48 h. After filtration the solvent was removed and the
oily residue was washed with hexane. The compound was
recrystallized from CH2Cl2 to produce 1.758 g (94% yield) of 5
as yellow crystals. 1H NMR (CDCl3, 300 MHz): δ 7.58-7.06
(m), 6.54 (s). 13C NMR (CDCl3, 300 MHz): δ 164.43, 134.77
(dd), 130.79, 130.11, 128.76 (dd), 127.94 (dd), 126.43, 124.54,
124.08, 117.93, 113.46, 90.63, 84.16. FT-IR (KBr): 2203(w),
1483(m), 1437(s), 1284(s), 1231(s), 1098(s), 781(m) cm-1. Anal.
Calcd for C55H40O2P2PtS2Cl2: C, 58.72; H, 3.58; S, 5.70.
Found: C, 59.16; H, 4.00; S, 5.70.
15668(81)
-6963(67)
15447(70)
20255(81)
23987(87)
C(4G) 38662(100)
C(4F) 34310(93)
C(3G) 31087(121)
24835(96) -11695(83)
43925(122)
67725(151)
63465(77)
23052(81)
16913(166) 1993(199)
23209(37)
8784(33)
C(5)
Cl
Cl(1)
C(3E)
C(4E)
S(1)
17019(98)
13095(46)
10944(37)
-127(98)
-2757(90)
52702(25)
45603(41)
47290(57)
2015(45)
1442(32)
884(75)
65283(45)
40034(113)
33500(122)
-54664(34)
-17690(58)
-6691(85)
9968(85)
13708(78)
42833(24)
64545(33)
65163(45)
38115(54)
859(73)
1010(21)
1090(33)
1107(50)
585(50)
S(2)
C(4I)
C(4H)
Electr och em ica l Mea su r em en ts. A three-compartment
electrochemical cell (∼25 mL capacity) was used for electro-
chemical measurements. A coiled Pt wire was used as a
counter electrode and separated from the working electrode
compartment by a glass frit. The reference electrode was Ag/
Ag+ (CH3CN, 0.1 M TBAP). The working electrode was a
platinum disk (diameter ) 5 mm). The concentration of 5 was
1.0 × 10-3 M in 0.10 M TBAP-CH2Cl2.
57854(58) -52023(100)
a
Equivalent isotropic U is defined as one-third of the trace of
the orthogonalized Uij tensor.
crystal measuring 0.4 × 0.4 × 0.4 was mounted on a glass
fiber and aligned on the diffractometer. Final unit cell
parameters were determined by least-squares refinement of
25 reflection with 20° < 2θ < 30°. Crystal data, data collection
and reduction, and structure refinement details are listed in
Table 1. Crystal stability was monitored by measuring three
X-r a y Cr ysta llogr a p h ic Da ta for 5. Crystals of 5 were
grown by slow concentration of a CH2Cl2 solution. A yellow

Notes
Organometallics, Vol. 15, No. 1, 1996 463
standard reflections every 97 measurements. Data were
corrected for Lorentz and polarization factors and reduced to
unscaled F values. Crystallographic calculations were per-
formed by using the Siemens SHELXTYLPLUS (PC version)12
program library. The positions of all non-hydrogen atoms were
determined by direct methods. Hydrogen atoms were included
using a riding model with d(C-H) ) 0.95 Å, and the isotropic
thermal parameters were fixed at 0.08 Å2. A disorder model
for sulfur atom S2 and carbon atom C4I was used. The final
agreement factors for the 3362 data (|Fo| > 4.0σ(|Fo|) were Rf
) 5.86 and Rwf ) 7.33 and GOF ) 1.14.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond lengths and angles, and anisotropic dis-
placement coefficients (17 pages). Ordering information is
given on any current masthead page.
(12) Nicolet Instrument Corp., Madison, WI, 1988.
OM950155T